The invention is concerned with methods and apparatus for materials processing involving a chemical and/or a physical action(s) or reaction(s) of a component or between components. Examples of processes that are encompassed by the invention are heating, cooling, agitation, reaction, dispersion, change of state including solution and emulsification, oxidation, reduction, blending, neutralization, change of shape, of density, of molecular weight, of viscosity or of pH. Other examples that are more specifically chemical reactions are halogenation, nitration, reduction, cyanation, hydrolysis, dehydroxation, epoxidation, ozonation diazotisation, alkylation, esterification, condensation, Mannich and Friedel-Crafts reactions and polymerization.
Apparatus for materials processing consisting of coaxial cylinders that are rotated relative to one another about a common axis, the materials to be processed being fed into the annular space between the cylinders, are known. For example, U.S. Pat. No. 5,370,999, issued Dec. 6, 1994 to Colorado State University Research Foundation discloses processes for the high shear processing of a fibrous biomass by injecting a slurry thereof into a turbulent Couette flow created in a xe2x80x9chigh-frequency rotor-stator devicexe2x80x9d, this device having an annular chamber containing a fixed stator equipped with a coaxial toothed ring cooperating with an opposed coaxial toothed ring coupled to the rotor. U.S. Pat. No. 5,430,891, issued Aug. 23, 1994 to Nippon Paint Co., Ltd. discloses processes for continuous emulsion polymerization in which a solution containing the polymerizable material is fed to the annular space between coaxial relatively rotatable cylinders under conditions such that Taylor vortices are formed, whereby a desired complete mixing condition is obtained.
My U.S. Pat. Nos. 5,279,463 (issued Jan 18, 1994) and 5,538,191 (issued Jul. 23, 1996) disclose methods and apparatus for high-shear material treatment, one type of the apparatus consisting of a rotor rotating within a stator to provide an annular flow passage comprising a flow path containing a high-shear treatment zone in which the passage spacing is smaller than in the remainder of the zone to provide a subsidiary higher-shear treatment zone in which free supra-Kolmogoroff eddies are suppressed during passage of the material therethrough.
Couette developed an apparatus for measuring the viscosity of a liquid consisting of a cylinder immersed in the liquid contained in a rotating cylindrical vessel, the viscosity being measured by measuring the torque that was thus applied to the cylinder. It was found that a linear relationship was obtained between the viscosity measurement and the angular velocity of the rotor surface up to a certain value beyond which the linear relationship broke down. This phenomenon was investigated by G. I. Taylor who showed that when a certain Reynolds number was exceeded the previously stratified flow in the annulus between the two cylindrical surfaces became unstable and vortices appeared, now known as Taylor vortices, whose axes are located along the circumference of the rotor parallel to its axis of rotation and which rotate in alternately opposite directions. The conditions for the flow to be become unstable in this manner can be expressed with the aid of a characteristic number known as the Taylor number, depending upon the radial width of the annular gap, the radius of the rotor and its peripheral velocity. Although for their special purpose Nippon Paint wishes Taylor vortices to be present, I have found that when using such apparatus for the types of process given above as examples, especially where thorough and uniform micro-mixing is required, the presence of the vortices inhibits the action or reaction desired since the material to be treated becomes entrained in the vortices and becomes partially segregated in the vortices whereupon mixing becomes incomplete and must be relied upon by much slower diffusion processes.
It is a principal object of the invention to provide new methods and apparatus for materials processing wherein such methods can be carried out, and the apparatus employed can be operated, without the presence of Taylor vortices so as to facilitate any mixing that is required.
It is a more specific object to provide such methods, and to provide apparatus for carrying out the methods, in which flow of the materials involved can be effected without the generation of Taylor vortices with their consequent inhibition of mixing.
In accordance with the present invention there is provided a new method for processing materials comprising passing the material to be processed in a flow path through an annular processing passage between two closely spaced smooth surfaces provided by respective cylindrical apparatus members rotating relative to one another;
wherein the radial spacing between the two surfaces is equal to or less than the back-to-back radial thicknesses of the two boundary layers of the material against the two surfaces; and
wherein the smoothness of the surfaces is such that formation of Taylor vortices in the processing passage is inhibited.
Also in accordance with the invention there is provided new apparatus for processing materials comprising two cylindrical apparatus members mounted for rotation relative to one another, and providing two closely spaced smooth surfaces providing an annular processing passage constituting a flow path for the material;
wherein the radial spacing between the two surfaces is equal to or less than the back-to-back radial thicknesses of the two boundary layers of the material against the two surfaces that is to pass in the processing passage; and
wherein the smoothness of the surfaces is such that formation of Taylor vortices in the processing passage is inhibited.